VFD on single phase - Electrician Talk - Professional Electrical Contractors Forum

RonR · 04-12-2007, 06:49 PM

The company I work for has a 1200 amp 240/120 single phase service feeding a step up xfmr with 480 volts on the secondary.(240/480)

when the VFD is running @ 40hz you can see a little bit of flicker from a regular light bulb, when the speed is increased to 43hz the flicker is so bad that people up the road several miles complain of the flickering.

the amperage bounces around so much that it is not possible to get a current reading with a conventional meter and we have no other meters.

We are pumping crude oil, 500-700 psi @ approx 200 barrel an hour.

What chance is there that this is being caused by Harmonics????

Would a harmonic filter help???

Any Ideas???

**MDShunk** · 04-12-2007, 07:00 PM

Sounds more like a capacity issue on the utility end.

John · 04-12-2007, 07:35 PM

Do you know if you have AC line reactors on the drive?

http://www.ab.com/drives/techpapers/...%20Drives1.pdf

brian john · 04-12-2007, 08:14 PM

5 issues.

1. By now all electriucians should be using True RMS meters.
2. Capacity as Marc said.
3. May well be harmonics 5,7, 11,13, 17,19 right up the line for a 6 pulse, if it is a 12 pulse then 11,13 23,25 35,37.
4. As John stated REACTORS
5. Are there any capicator banks installed on site or in the utility distribution substation.
You could use a line disturbance analyzer to determine all but item 4. Item 4, read the specs and do a visual.

brian john · 04-12-2007, 08:15 PM

5 issues DUH could not edit?????

**frenchelectrican** · 04-12-2007, 09:13 PM

I am not sure if this is related sisuation with the VFD's if you ran that on single phase supply. IF so you have to derated the VFD's because the timming sequnce between normal AC and VFD's AC current is not match up and it will " bounce " around to get it running right.

but as other suggest about the sisuation they are right on the bat with it and possiblty the POCO cans can be smaller than it should be it can do funny thing as well.

The other thing if the VFD controller is quite a way from motor with long line feeding the motor it can act like capaitior or other fancy word which i can't find this in plain jane english [ sorry about that ]

and other thing but i don't think this will be related or not depending on the VFD set up is the feedback control because if the feedback control connection at the VFD termail area and the lines are pretty long it will do a funny thing but you have feedback control connected at motor end it may be little better [ this part i am not sure if that can cause irreguar singal feedback ]

Merci, Marc

ILSS · 04-12-2007, 10:42 PM

You will not be able to read the current at the output of the VFD with a meter because it is a Pulse Width Modulated output.

**frenchelectrican** · 04-12-2007, 10:46 PM

ILSS;

I was well aware with that but the sure fire way to read the current is using the true RMS ampmeter [ just make sure that True RMS meter can read from few HZ up to apx 180 or so depending on the type of meter ]

but if you use the ave reading ampmeter on VFD's just throw that crap out of the " window " that will never work at all.

Merci , Marc

RonR · 04-13-2007, 06:28 AM

The VFD has built-in line reactors.

The power company says a filter will not help.

There are no capacitor banks, just a standard transformer on a pole directly from the primary lines.

brian john · 04-13-2007, 07:27 AM

Quote:

You will not be able to read the current at the output of the VFD with a meter because it is a Pulse Width Modulated output

When you are concerned about harmonics output current is not the concern VFD input and more importantly in this case at the Point of Common Coupling (service) with the utility and at the neighbors service.

Had the exact same issue two years ago with a large printing press, the reactors were not connected properly. Look for reactor size, working properly, wired per the manufacture specs. Do not necessarily believe the utilities, drive around look for substations near this facility.

Do you have access to a disturbance analyzer?

RonR · 04-13-2007, 07:50 AM

The reactors are factory installed INSIDE the VFD. the power companies installation is new, there are no substations nearby.

I think it is several miles to the substation.

we do not have a disturbance analyzer. Our engineer ordered a $10,500 filter without doing any type of power study.

Shouldn't there have been some kind of analysis BEFORE anything was ordered???

Ron

mgalaviz · 08-04-2007, 02:13 PM

is transformer grounded.

RonR · 08-04-2007, 06:23 PM

yes, it is grounded.

since i posted this thread, the VFD totally burned up on the inside.

the mfgr. said that if the VFD is powered up but not drawing current, the dc buss voltage will continue to increase.